Structural Changes of Compacted Soil Layers in Northeast China due to Freezing-Thawing Processes

Soil compaction has become a global concern that reduces soil quality and may jeopardize agricultural sustainability. The objective of this study is to evaluate if the freezing–thawing process can alleviate the negative effects of soil compaction during overwinter time in Northeast China. The field experiment was a split plot design including two surface treatments (bare and mulch) and three compaction levels (low, moderate, and high compactions with initial bulk densities of 1.2, 1.4 and 1.6 g cm−3). Results showed that compared with initial values in the fall, freezing–thawing events increased soil porosity (by 4.28% to 25.68%) and the ratio of large-size pores (by 44.5% to 387.6%) after thawing in the spring. The greatest changes were observed in the high compaction treatment, and mulch-enhanced soil structural transformation. Additionally, the ratio of large-size aggregates (>1 mm) was increased and the fraction of small-size aggregates (